The present invention relates to improvements in apparatus for making X-ray images without resorting to X-ray film, and more particularly to improvements in ionography imaging chambers of the type wherein a dielectric receptor sheet or an analogous insulating charge-receiving medium is placed into an interelectrode gap which is defined by an anode and a cathode and contains a high Z gas. During imaging, the gas is maintained at an elevated (superatmospheric) pressure and serves to absorb incident X-rays.
In an imaging system of the above outlined character, the compressed high Z gas (e.g., Freon, Krypton or Xenon) plays the important role of absorbing X-rays to effect the generation of a charge by a quantum process, such as the photoelectric or Compton effect. The thus produced charge results in development of a latent electrostatic image on the dielectric sheet which is located in the electric field between the electrodes. The latent image on the sheet is made visible by an electrostatic technique including the deposition of toner particles.
In order to achieve a satisfactory yield as well as to reduce the exposure of patients to X-rays, presently known ionography imaging chambers are operated at a gas pressure of 6-20 atmospheres. Thus, the walls of the imaging chamber must withstand a very high internal pressure. At the same time, such walls (and especially the wall which extends across the path of incident X-rays) must be sufficiently thin to minimize absorption and/or lateral diffusion (scattering) of X-rays. Therefore, conventional imaging chambers employ a relatively thin membrane or pane which consists of beryllium and is inserted into a window provided in the front wall or lid of the chamber. The marginal portions of the membrane are clamped in a solid frame which is installed in the window. That portion of the front wall which surrounds the window and receives and retains the frame is rather strong and bulky. Moreover, the membrane is expensive, not only because of the cost of its material but also because the material is brittle so that it must be machined with great care. The means for securing the membrane to the frame, for securing the frame to the front wall, and for securing the front wall to the rear wall or base of the imaging chamber comprises a large number of screws or analogous fasteners which interfere with access to the interior of the imaging chamber during assembly, insertion and/or maintenance of its component parts.